Increased serum level &/or toxicity w/ ketoconazole (CYP3A4 inhibitor). Potentially increased serum levels w/ amiodarone, cimetidine, clarithromycin, delavirdine, diltiazem, dirithromycin, disulfiram, fluoxetine, fluvoxamine, grapefruit juice, indinavir, itraconazole, nefazodone, nevirapine, propoxyphene, quinupristin-dalfopristin, ritonavir, saquinavir, verapamil, zafirlukast, zileuton. Improved response to inhaled corticosteroids w/ addition of salmeterol. Decreased serum levels w/ St. John's Wort (CYP3A4 inducer).